The present invention is related to an optical sensor system on an apparatus for treating liquids.
An optical sensor system of the type of the present invention serves for the determination of the height of a liquid level in vessels (reaction vessels or wells of microtiter plates, for instance), of the position and the identity of vessels (reaction vessels or microtiter plates, for instance) and of the position and the identity of objects (e.g. tools, accessories, pipette points in a rack and other so-called “labware” in an apparatus for treating liquids.
In particular, an apparatus for treating liquids can be an apparatus for metering and/or transporting and/or examining and/or processing (chemically, physically or biologically) liquids. In known apparatuses for treating liquids, the processes are performed either manually or partly or completely automatically. For instance, manual pipettes, PC-supported metering systems and completely automatic metering stations are known for metering. There are completely automatic treatment stations for metering, transporting, examining and processing liquids (so-called “workstations”)
When pipetting manually as well as when pipetting automatically, the pipette point has to be dipped into the liquid with an immersion depth as small as possible, because the metering error increases with the immersion depth, and because the pipette point or the vessel, respectively, might be damaged upon too deep an immersion. In addition, the pipette point must be continuously submerged during the pick-up of liquid, so that no air is aspirated. In doing so, it has to be taken into account that the liquid level in the vessel decreases when picking up liquid. With manual pipettes, the user has to check the immersion depth of the pipette point continuously and to follow up with the pipette point. In automatic metering apparatuses, monitoring and control devices are used for this.
From EP 1 288 635 A2, the entire contents of which is incorporated herein by reference, an apparatus for treating liquids with an illumination device for illuminating an approximately point-shaped illumination position in space and an approximately point-shaped light receiving device with a photo detector for supplying a measurement signal depending on the intensity of the received light is known. The apparatus has an imaging system for imaging the illumination position on the approximately point-shaped light receiving device. Further, it has an analysing device for monitoring the approach of an interface between two media with different refractive indices to the illumination position, by analysing the measurement signals furnished by the photo detector. When an interface between two media with different refractive indices enters into the illumination position, the intensity of the light radiation received by the light receiving device and thus the measurement signal supplied by the photo detector changes strongly. Thus, it can be determined whether there is an interface in the illumination position or not.
Because the light beam of the illuminating device and the imaging system can be coaxially aligned towards the illumination position, touch-free retrieval of interfaces from a greater distance and with significantly less lateral space demand is possible. This promotes the retrieval of the liquid level in vessels with relatively small opening and/or relatively great depth.
It can be selectively worked with light of a wavelength for which a liquid (water e.g.) is un-transparent, in order to retrieve a liquid level free from disturbances through vessels nearby.
For the determination of the position of an interface, the relative position of illumination position and interface can be varied, until the interface is situated in the illumination position. Further, it is possible to scan the surface of an object with the illumination position, in order to deduce the position of the entire object and/or its identity based on individual values or on the course of the measurement signal. In order to do this, the apparatus may have an adjustment device for adjusting the relative position of illumination position and interface in the direction of the optical axis of the imaging system and/or transversely to it. The analysing device can trigger the adjustment of the relative position of illumination position and interface by the adjustment device. Then, the adjustment can take place depending on measurement signals, for instance in order to set the illumination position to the interface and/or to move it along the interface.
For positioning the illumination point on the interface or for finding the interface, respectively, the adjustment device must often run through long movement paths. This is very time-consuming and decreases the working speed of the apparatus for treating liquid.
Starting from this, the present invention is based on the objective to provide an optical sensor system on an apparatus for treating liquids and a method for operating such an optical sensor system which allows a more rapid detection of interfaces.